CS257745B1 - Method of thermogravimetric determination of medium degree of condensation of higher linear phosphates of divalent metals Men / 2H2Pn ° 3n + 1 - Google Patents

Abstract

The method uses thermal recrystallization of higher linear phosphates to form cyclotetraphosphates and release chemically bound water, the mass of which is determined. From it, the average degree of condensation of higher linear phosphates can be calculated based on stoichiometry. When determining, it is advantageous to work at temperatures as close as possible to the recrystallization temperature. The solution can be applied in phosphate chemistry and technology, in assessing the quality of phosphate pigments or the quality of long-term microelement fertilizers based on higher linear phosphates of divalent metals.

Description

The present invention relates to the thermogravimetric determination of the mean degree of condensation of the higher linear phosphates of divalent metals of the general formula O-,. _.

n / 2 2 n 3n + 1

II

The higher linear divalent metal phosphates represented by the general formula ^Μβ η / 2 ^ 2 ^Ρ ηθ3η + 1 are glassy amorphous products. They have anions arranged in long chains to which the individual tetrahedra (PO ^) are linked by POP bonds. It is believed that the chains may contain these joined tetrahedra from a few tens up to 10 ^. Their number then expresses the length of the chain and the degree of condensation, which corresponds to the index n in the formula ^Me n / 2 ^H 2 ^P n ^G 3n + l *

Determining the chain length - condensation stage, at least approximately, is not yet practically possible. So far, the methods used for this purpose have been attempted and have not produced satisfactory results. In general, the most widespread method for the qualitative and sometimes quantitative evaluation of condensed phosphates is chromatography. However, this is unsuitable for this purpose since it necessitates the transfer of samples into solution. On dissolution, however, the hydrolytic cleavage of long phosphate chains and their decomposition can generally be prevented, as a rule, into hydrogen-oligo-phosphate anions having chains of less than 10 members. However, even if it is possible to prevent hydrolytic cleavage (which is not possible) from dissolving the higher linear phosphates, there are not yet chromatographic agents that would allow the anions to be separated (and thus their length determined) with chains of more than 10 members.

Similarly, nuclear magnetic resonance imaging (IRMR) methods, which in most cases require the sample to be dissolved. Non-destructive analytical methods such as X-ray diffraction analysis, IR spectroscopy, Raman spectroscopy, or luminescence spectroscopy are also not applicable. X-ray diffraction analysis is not an option at all, since the higher linear condensed divalent metal phosphates are amorphous, non-crystalline in nature and therefore do not provide any diffraction lines necessary for their evaluation. Although IR and Ramen spectroscopy can generally be distinguished qualitatively higher linear phosphates in addition to other types of condensed phosphates, their absorption bands are not so characteristic that they can be used to determine the chain length.

The use of luminescence methods to determine the chain length - condensation degree - of higher linear phosphates was also proposed and verified. However, these assays require large amounts of calibration measurements, in addition with substances that have a precisely characterized chain length; however, this is virtually impossible on the basis of what has been said above. Moreover, according to the experience of the present inventor, their metal cations significantly contribute to the luminescence properties of the condensed phosphates, which would further undermine the accuracy of the measurements.

These drawbacks are eliminated by the invention thermogravimetric determination of average degree of condensation of higher linear phosphates divalent metal ^Me n / 2 ^H 2 ^ n ° 3n + l ^{characterized considerably} characterized in that a pattern of higher linear phosphates with, preferably by milling, precalcined at a temperature higher than 200 ° C, but below its recrystallization temperature, preferably at a temperature as close as possible to the recrystallization temperature, its mass (mJ) is determined and thereafter the sample is thermally recrystallized to convert to cyclotetaphosphate by calcination to a temperature greater than its recrystallization temperature ,. but below its melting temperature, preferably to a temperature as close as possible above the recrystallization temperature and again determining the weight (m _9). the difference of two determined masses (m _n -m m = ₉₎ corresponds to * ¹ II chain groups of the original higher linear divalent metal phosphate ^Μθ Π) / 2 ^ 2 ^{Ρ η Ο 3η} + 1 and can therefore be calculated from the value of n as the average degree of condensation according to the formula n = 72 .M molecular weight compound resulting from recrystallization starting higher C 4 Me 2 ^T 12 ^υ linear phosphate which is cyclo -tetrophosphate of the respective divalent metal.

Thorough drying of the sample is necessary because the loss of water in the form of moisture only at the actual cleavage to recrystallization would entail an error in the determination. In addition, some of the higher linear phosphates are hygroscopic, so that if they are stored for a long time in a normal humid atmosphere, especially when they are in powder form, the proportion of water present can be considerable. Therefore, it is also effective to dry the sample by precalcinating at a temperature of at least above 200 ° C, the closer the temperature to the recrystallization temperature, the more efficient drying is of course.

It is also advantageous for the sample to be ground in advance, since drying (and recrystallization itself) is facilitated. The dried sample is allowed to cool in the decanter (as it could otherwise absorb moisture again upon cooling) and its weight (m ^) is determined. Thereafter, the sample is subjected to thermal recrystallization to release water bound as the terminal hydroxy groups of the higher linear phosphate chains. Based on the determination of the amount of this water, respectively. the number of water molecules bound in this way, the mean degree of condensation of the higher linear phosphates can then be determined.

It is utilized that these phosphates are able to convert, mostly quantitatively, by thermal recrystallization to cyclo-tetraphosphates according to the equation:

^Me n / 2 ^H 2 ^P n ° 3n ₊ l = ^{n / 4} - ^Me 2 ^P 4 ° 12 ° ^{+ H} 2 ^(1>

Recrystallization is an exothermic event and occurs for higher linear phosphates of individual bivalent metals at temperatures in the range of 400 to 700 ° C. It is advantageous for the determination to use recrystallization temperatures as close as possible to the recrystallization temperature itself, since a further increase in temperature could in some cases influence the result by releasing part of the phosphorus component into the gas phase. However, temperatures higher than the melting point of the sample (which corresponds to the melting point of the cyclo-tetraphosphate of the respective bivalent metal) cannot be used at all, since the melting of the sample binds water molecules from the atmosphere, again changing the weight of the sample.

After recrystallization, the weight of the sample cooled in the desiccator (n opět) is again determined and the mean degree of condensation of the starting higher linear phosphates is calculated. The formula for its calculation is based on the chemical equation (1) expressing the process of recrystallization.

To determine the required values -, m ₂ , resp. A m can also be successfully used thermoanalytical methods - thermogravimetry under special conditions. To achieve sufficient accuracy, relatively large sample weights (at least 3 g) need to be used, which is not common in commercial thermal analysis instruments, while utilizing the maximum TG sensitivity. Furthermore, in the thermal analysis, it is necessary to predetermine the appropriate heating rates so that the value (expressing the sample weight just before recrystallization) and the value of m ₂ (sample weight just after recrystallization) can be read off when the sample weights are stable.

«

The invention further provides that in the case where the recrystallization of the higher linear divalent metal phosphates to form cyclotetaphosphates does not proceed entirely quantitatively, the final recrystallized product is subjected, preferably after regrinding, leaching with 0.1 M hydrochloric acid for a period of time. It is then washed with distilled water, separated quantitatively (by filtration, sedimentation) and its mass (m <+>) is determined. From the ratio m-j / mj, the degree of recrystallization of the higher linear phosphates to the cyclo-tetraphosphate is multiplied by multiplying the value n by the specification.

The result then gives the true mean degree of condensation of the starting higher linear divalent metal phosphates. This specification should be used, for example, in determining the mean degree of condensation of higher linear zinc phosphates in which the thermal recrystallization does not proceed entirely quantitatively. Indeed, part of the original sample remains in the form of higher linear phosphates and only a part recrystallizes to form disodium cyclophosphate. This fraction should be determined (and specified n), since it relates only to stanovené m determined according to point 1 of the invention.

The advantages of the method according to the invention lie in the precision, simplicity and unpretentiousness of the method.

It can be used to determine the mean degree of condensation - chain length - of higher linear divalent metal phosphates, which has not been practically possible so far. The method does not require special instrumentation or trained personnel.

Below are examples of using the method to determine the mean degree of condensation of higher linear divalent metal phosphates.

Example 1

Higher linear cobalt phosphates of the formula ^Co n / 2 ^ř 12 ^P n ° 3n + 1 as a glassy amorphous substance are ground and dried for 1 hour at 430 ° C. After cooling in a desiccator, exactly 100 g of dried sample was weighed and then calcined in a platinum dish for 1 hour at 620 ° C.

After cooling in the desiccator, its weight was determined to be 99.908 1 g. From a value of Λ ni = 0.0919 g, the mean condensation degree for a starting higher linear cobalt phosphate of 180.6 was calculated.

Example 2

Higher linear manganese phosphates of the general formula ^Μη η / 2 ^ 2 ^Ρ η ° 3η + 1 as a glassy amorphous substance are ground and dried for 1 hour at 410 ° C. After cooling in a desiccator, exactly 200 g of dried sample was weighed and then calcined in a platinum dish for 1 hour at 600 ° C.

After cooling in a desiccator, its weight was determined to be 199.875 g. The mean condensation degree for a starting higher linear manganese phosphate equal to 272.3 was calculated from a value of m m - 0.124 2 g.

Example 3

The higher linear zinc phosphates of the formula ^Zn n / 2 ^H 2 ^P n ° 3n + 1 are ground as a glassy amorphous substance. The weighing of about 3 g was transferred to a platinum crucible and subjected to thermal analysis on a Derivatograph Ql 500 (J. Paulik, F. Paulik,

L. Erdey). The heating rate was selected at 5 ° C / min, the TG sensitivity was 20 mg. After recording the exothermic recrystallization process (with a maximum at 262 ° C) on the DTA curve, the thermal analysis was terminated. On the TG curve, it was read that the sample had a weight of 3.007 3 g just prior to recrystallization and its weight decreased by 0.002 1 g after recrystallization.

From these values, a mean degree of condensation of 230.8 was calculated. Since the recrystallization did not proceed quantitatively, the sample was ground after thermal analysis and the accurately weighed 2 g was subjected to leaching with 0.1 M hydrochloric acid (250 ml) for 2 h. ·

After leaching, the solid phase was collected by filtration on a pre-weighed glass frit (S 3), washed and dried at 150 ° C ... Then the solid phase weight was determined to be 1.754 g. After dividing this final weight by the leaching weight, a factor of 0.877 was obtained. , which multiplied the value of the mean condensation stage determined by thermal analysis. A mean degree of condensation of the higher linear zinc phosphates of 202.4 was thus obtained.

Claims (2)

SUBJECT OF THE INVENTION 1. Method of thermogravimetric determination of the mean degree of condensation of higher linear phosphates of divalent metals ^M % / 2 ^H 2 ^P n ° 3n + 1 ⁱⁿ Y ^, characterized in that the sample of higher linear phosphates is precalcinated, preferably after grinding, at a temperature higher than 200 ° C, but below its recrystallization temperature, preferably at a temperature as low as recrystallization temperature, its mass m is determined, and then the sample is thermally recrystallized by converting to cyclotetaphosphate by calcination to a temperature above its recrystallization temperature but below its melting point, preferably to a temperature as close as possible to its recrystallization temperature, its weight is again determined> wherein the difference of two fixed weights & m = ^m i- ^m 2 corresponds to the water bound in the form of terminal hydroxyl groups of the original Cu-řetěz257745 higher linear divalent metal phosphate ^{β η} / 2®2 ^{Ρ ηθ3η} + 1 ° ^and YP ^ i ^t 4, the value of n as the average degree of condensation according to the formula wherein M is the molecular weight of the compound resulting from recrystallization i.e. cyclo-tetraphosphate respective divalent metal. 2. Process according to claim 1, characterized in that in the case where the recrystallization of the higher linear divalent metal phosphates to form cyclotetaphosphates does not proceed quantitatively, the final recrystallized product, preferably after grinding, is subjected to leaching with 0.1 M * hydrochloric acid for at least 1 hour, then washed with distilled water, quantitatively separated, dried and weighed m ₃ , the m / m ratio indicating the degree of recrystallization of the starting higher linear phosphates to cyclotetaphosphate and therefore multiplying the value by n to refine the determination .